Phytotoxicity of Phthalate Plasticisers: 2. SITE AND MODE OF ACTION

The effects of phthalate esters on chlorophyll a₂ fluorescencein radish plants (Raphanus sativus L. cv. Cherry Belle) wereexamined Fluorescence yield was increased in those plants exposedto an aerial concentration of 120 ng dm^–3 dibutyl phthaiatc(DBP) at a rate of 3.0 dm³ min^–1 for 13 d. Comparisonof fluorescence enhancement ratios and F_red/F_ox, suggests thatDBP inhibits photosynthesis in radish plants at a site afterQ_A. Both DBP and diisobutyl phthalate (DIBP) strongly inhibiteduncoupled (PS2+PS1) electron transport rates in thylakoids isolatedfrom spinach. At a chlorophyll concentration of 10 µgcm^–3 the concentrations of DBP and DIBP exhibiting 50%inhibition were 44 mmol m^–3 and 42 mmol m^–3 respectively.Basal electron transport rates were also inhibited, with 87mmol m^–3 of DBP or DIBP producing 50% inhibition. Measurementof photosystcm 1 activity suggested that the main site of actionof these phthalates was localized at a site near the reducingside of photosystem 2. Key words: Phthalate, plasticiser, chlorophyll, fluorescence, photosynthesis, inhibition     

DISCONTINUOUS MITOCHONDRIAL AND CHLOROPLAST LARGE SUBUNIT RIBOSOMAL RNAs AMONG GREEN ALGAE: PHYLOGENETIC IMPLICATIONS1

To provide insights into the occurrence, evolution, and phylogenetic distribution of discontinuous mitochondrial and chloroplast large subunit ribosomal RNAs (LSU rRNAs) among green algae, we surveyed 12 taxa representing three classes of green algae: the Chlorophyceae, Pleurastrophyceae, and Micromonadophyceae (sensu Mattox and Stewart 1984). We present evidence that discontinuous mitochondrial and chloroplast LSU rRNAs are quite widespread among green algae. Mitochondrial LSU rRNAs appear discontinuous in zoosporic chlorophycean lineages displaying a clockwise or directly opposed configuration in their flagellar apparatus, as well as in chlorococcalean autosporic taxa phylogenetically related to them, but are continuous among zoosporic green algal lineages with a counterclockwise flagellar apparatus configuration, as well as among chlorococcalean autosporic taxa phylogenetically related to them. Chloroplast LSU rRNAs appear discontinuous in all of the lineages investigated. Discontinuous mitochondrial LSU rRNA represents a molecular trait that might have originated at or near the base of Chlorophyceae, whereas discontinuous chloroplast LSU rRNA might have developed very early in the evolutionary history of the green algal group itself. We suggest, therefore, that the presence of discontinuous mitochondrial but not chloroplast LSU rRNA can be used as an additional character in assessing phylogenetic affiliations among green algae.     

WOOD ANATOMY OF TREMANDRACEAE: PHYLOGENETIC AND ECOLOGICAL IMPLICATIONS

Stems of four species of the Australian family Tremandraceae furnished sufficient material for analysis of wood anatomy. Presence of simple perforation plates on vessel elements, occurrence of libriform fibers (some septate), tendency toward vasicentric parenchyma, presence of crystalliferous axial parenchyma strands, presence of crystals singly in ray cells, and occurrence of amorphous deposits in parenchyma are all features in which Tremandraceae resemble Pittosporaceae. Wood anatomy tends to support a “rosoid” rather than a sapindalean, rutalean, or polygalalean affinity for Tremandraceae, although wood is only a preliminary indicator. By the use of numerical indices as well as such indicators as helical thickening and presence of vascular tracheids, wood of Tremandraceae is shown to be highly xeromorphic. The genus Tremandra may represent a secondary entrant into wet forests of southwestern Australia; it clearly is not relict from mesic ancestry.     

嵌套性:研究方法、形成机制及其对生物保护的意义

岛屿或者“生境岛”中的生物区系常常显示出一种嵌套结构 ,即物种较贫乏的岛屿中的物种是物种较丰富的岛屿中的物种的一个适当的子集 ,如果将各个岛屿中的生物区系排列起来就形成一个嵌套的序列。与种 面积关系一样 ,嵌套结构在很多生境类型和生物类群中也都存在。嵌套性对生物保护也有一定的意义 ,特别是与SLOSS争论 (是单个大的还是几个小的保护区能保护更多的物种 )有一定关系。在过去的十几年中 ,已经提出了一些方法 ,可以对嵌套性进行定量刻画和统计检验。同时 ,对嵌套性的形成机制也进行了大量的研究 ,其中选择性的迁移和选择性的灭绝是两个主要的原因。由于嵌套性分析只需要物种的存在 /不存在数据 ,使得很多调查数据都能够利用起来 ,因此 ,这是一个值得深入研究的领域     

POLYPLOIDY AND DIPLOIDY: NEW PERSPECTIVES ON CHROMOSOME PAIRING AND ITS EVOLUTIONARY IMPLICATIONS

The last widely accepted classification of polyploidy recognized three major categories: autoploidy, segmental alloploidy, and true alloploidy. Criteria for recognizing these types were based largely on chromosome pairing in F₁ hybrids, but until very recently there were no quantitative criteria to distinguish autoploids from segmental alloploids. This is theoretically possible, and Jackson and Casey (1982) and Jackson and Hauber (1982) have presented models and methods to quantitatively predict the frequencies of the different meiotic configurations in autotriploids through autooctoploids. The expected numbers of configurations then can be statistically tested for goodness of fit with observed data. Synthetic and natural autotetraploids have been shown to fit the models well. However, the exceptions that do not fit are of particular interest because they indicate the presence of Ph-like (Pairing homoeologous) genes that cause fewer multivalents and more bivalents than expected in the autoploid models. The effect of Ph-like genes at the nuclear level apparently involves placement of chromosome attachment sites on the nuclear membrane such that different genomes occupy slightly different sites. This would be far enough apart in true alloploids so that no pairing occurred in the original F₁ hybrid. In true autoploids and normal diploids, homologues are equally close so that pairing obeys probability laws that make it possible to describe expected pairing events with appropriate models and equations. From the foregoing statements, one can deduce that the terms autoploid, segmental alloploid, and true alloploid need not and indeed should not be equated with results of crosses between any taxonomic levels. Rather, they represent conditions that can be attained by one or very few genes acting on nuclear membrane attachment sites. It is possible to deduce from hybrids at the diploid level the type of polyploid that can be obtained, and such data can have great agronomic value. A generally held dogma is that the inability of chromosomes to pair in F₁ hybrids is due to considerable genetic divergence and perhaps numerous structural changes at the light microscope and/or ultrastructural level. Data from various sources show that this need not be true, and there is no reason to believe this is a factor in what has been called genome divergence in the classical sense. Genome divergence in terms of pairing ability can occur at the population level due to one or a few genes.     

EARLIEST MEGAFOSSIL EVIDENCE OF FAGACEAE: PHYLOGENETIC AND BIOGEOGRAPHIC IMPLICATIONS

Fossil evidence of Fagaceae from the Paleocene/Eocene boundary of western Tennessee is described and discussed. These fossils include a newly discovered pistillate inflorescence and dispersed fruits of subfamily Castaneoideae as well as a taxon that resembles modern trigonobalanoids (pistillate inflorescences and dispersed mature fruits). Fossil staminate catkins with fagaceous pollen, which we suggest may be conspecific with the trigonobalanoid infructescences, are also found at the locality. Two distinct types of fagaceous leaves are present at the locality. The reproductive structures are the oldest megafossils unequivocally assignable to Fagaceae and represent the oldest remains of subfamily Fagoideae and the oldest megafossil remains of Castaneoideae. In addition, the fossils provide insights into the chronology of diversification, biogeography, and phylogeny of Fagaceae. The trigonobalanoid remains may also provide insights into the timing and circumstances of the evolution of wind pollination in Fagaceae.